Behavior and Safety Aspects of the Fast Reactor

Dynamic Behavior and Safety Aspects of the Fast Reactor 

Owing to the absence of moderator, the neutron lifetime I lies within the range 10 s for the fast reactor, compared to a typical thermal reactor 

The effective delayed neutron fraction, p, is not only smaller for a plutonium-fueled fast reactor than for a uranium-fueled thermal system iP = 0.(X)21 for Pu, p = 0.0065 for but is also more difficult to predict accurately because of the relatively large number of isotopes (including fertile species such as and Pu ) which may be making a significant contribution to the delayed neutron population. Taking into account the effect of the fast fission in which has a delayed neutron fraction of 

The use of gas cooling, with the consequent high primary circuit pressure compared with a sodium-cooled reactor, increases the probability of a loss-of-coolant accident. With a prestressed concrete pressure vessel however, the only mechanism which could lead to a rapid depressurization is the failure of one of the penetration seals into the vessel. The maximum rate of depressurization can be limited by flow restrictions built into the penetration closures, and the reactivity worth of the helium is typically well below the delayed neutron fraction, so that reactivity transients are not a problem. A reliable emergency heat removal system, independent of the main cooling system, is essential. 

Another possible fault in a gas-cooled fast reactor is leakage from the steam generator tubes, leading to an ingress of steam into the reactor core. 

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